Everytime I start my engine when cold it blows carbon out the exhaust. It is a new rebuilt engine, mid summer maybe 10 hrs. I replaced the exhaust with a new system but still the same water muffler and piping to the transom but from the water muffler to the engine is new or rebuilt. I have changed the oil a couple of times and it is black. It never use to be. The engine also stalls if not sufficiently warmed up.
Anyone Have a clue whats going on. Heres a pic of the crud, not good for the ocean Thanks

That is most likely a too-rich condition at some point during startup. Can you give a very detailed description of your cold start procedures?
Some report that they need a few minutes of running on choke to warm the engine enough to go without. My own experience is just a few seconds of running with choke and slowly(10-15 seconds) pull choke off; then a few minutes to warm it up before sailing.

My girl did that for a period. A series of tweaks fixed it -- re-setting timing (fuel wasnt being properly ignited) and making sure fuel system (clamps etc) was tight with no air leaks - otherwise i had to run with choke partially on.

Now choke only reqd for a few seconds. It seems off that you have to engage your choke for so long

Agree with the running rich diagnosis.
Suggest that you check your choke is working properly - full open to full closed. If it's not opening all the way...
Any idea what main jet is in the carb? I've gone with adjustable main jet, which allows me to adjust the mixture at full throttle. I find a bit lean is good.
Curious about the black oil. Did the rebuild include new rings? Was it done by a reputable shop? Could be that the new rings just haven't seated yet. Are you getting smoke out of the filler/out of the flywheel cover?
You've definitely got issues that need correcting.

Curious about the black oil. Did the rebuild include new rings? Was it done by a reputable shop? Could be that the new rings just haven't seated yet. Are you getting smoke out of the filler/out of the flywheel cover?
.

I thought about this also.
Fstued:
Describe how you have been breaking the newly rebuilt engine in. Perhaps the rings are not seated.
A few runs of an hour or more at cruise RPM varying the RPMs every once in awhile would be a good idea. Perhaps Russ or another member have some more specific\accurate guidlines for break in.

Some great ideas here. I thought about the choke being the problem but I haven't checked it yet, Lazy. I did go through and tighten all the full connections because of a gas odor.
Thanks for all the good info I hope I get time to work on it today

Was the dry side of the manifold cleaned during the rebuild? The MC has kicked out carbon, as seen in the pic, but very rarely and usually after an extended layup. What do the plugs look like?
Dan S/V Marian Claire

When we first got our new motor we had the same issue.
It was quite embarrassing at the anchorage!
I have started using the higher octane gas and hotter plugs and less marvels.
I think I was using too much of the fuel additives.
I haven't had the issue since we splashed her in October and we are running daily.
I'm no mechanic but it seems to be working.